Editing International Space Station (section)

===Altitude and orbital inclination===
{{multiple image |align=right |total_width=400
 |image1=Altitude of International Space Station.svg|caption1=Graph showing the changing altitude of the ISS from November 1998 until November 2018
 |image2=Animation of International Space Station trajectory.gif |caption2=Animation of ISS orbit from 14 September 2018 to 14 November 2018. Earth is not shown.
}}

The ISS is currently maintained in a nearly circular orbit with a minimum mean altitude of {{convert|370|km|mi|-1|abbr=on}} and a maximum of {{convert|460|km|mi|-1|abbr=on}},<ref name="nasa-iss-overview">{{Cite web|url=https://www.nasa.gov/international-space-station/space-station-overview/|title=International Space Station Overview|last=Garcia|first=Mark|date=28 April 2016|publisher=[[NASA]]|access-date=28 March 2021|url-status=live|archive-url=https://web.archive.org/web/20231120175258/https://www.nasa.gov/international-space-station/space-station-overview/|archive-date=20 November 2023}}</ref> in the centre of the [[thermosphere]], at an [[inclination]] of 51.6 degrees to Earth's equator with an eccentricity of 0.007.{{citation needed|date=April 2024|reason=eccentricity is changing over time, heavens-above.com is reporting 0.0004733 as of 8 April 2024.}} This orbit was selected because it is the lowest inclination that can be directly reached by Russian Soyuz and Progress spacecraft launched from [[Baikonur Cosmodrome]] at 46° N latitude without overflying China or dropping spent rocket stages in inhabited areas.<ref name="MCC Answer">{{cite web|last=Cooney|first=Jim|title=Mission Control Answers Your Questions|url=http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|url-status=dead|archive-url=https://web.archive.org/web/20090627185009/http://spaceflight.nasa.gov/feedback/expert/answer/mcc/sts-112/09_04_12_54_17.html|archive-date=27 June 2009|access-date=12 June 2011|quote=Jim Cooney ISS Trajectory Operations Officer|location=Houston, Texas}}</ref><ref>{{Cite book|last=Pelt|first=Michel van|title=Into the Solar System on a String : Space Tethers and Space Elevators|publisher=Springer New York|year=2009|isbn=978-0-387-76555-6|edition=1st|location=New York, New York|page=133}}</ref> It travels at an average speed of {{convert|28000|km/h|mph|-3|abbr=}}, and completes {{Orbit|daily orbits|15.5}} orbits per day (93 minutes per orbit).{{Orbit|ref|<ref name="heavens-above" />}}<ref name="tracking">{{Cite web|url=http://spaceflight.nasa.gov/realdata/tracking/index.html|title=Current ISS Tracking data|date=15 December 2008|publisher=[[NASA]]|access-date=28 January 2009|url-status=dead|archive-url=https://web.archive.org/web/20151225022741/http://spaceflight.nasa.gov/realdata/tracking/index.html|archive-date=25 December 2015}} {{PD-notice}}</ref> The station's altitude was allowed to fall around the time of each NASA shuttle flight to permit heavier loads to be transferred to the station. After the retirement of the shuttle, the nominal orbit of the space station was raised in altitude (from about 350&nbsp;km to about 400&nbsp;km).<ref name="nsf-20110620">{{Cite news|url=https://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/|title=Europe's ATV-2 departs ISS to make way for Russia's Progress M-11M|date=20 June 2011|access-date=1 May 2012|url-status=live|archive-url=https://web.archive.org/web/20230811170911/https://www.nasaspaceflight.com/2011/06/europes-atv-2-depart-iss-make-way-russias-progress-m-11m/|archive-date=11 August 2023|work=[[NASASpaceFlight.com]]}}</ref><ref name="Popular Mechanics">{{Cite magazine|first=Rand|last=Simberg|date=29 July 2008|title=The Uncertain Future of the International Space Station: Analysis|url=http://www.popularmechanics.com/science/air_space/4275571.html|url-status=dead|magazine=[[Popular Mechanics]]|archive-url=https://web.archive.org/web/20090331140838/http://www.popularmechanics.com/science/air_space/4275571.html|archive-date=31 March 2009|access-date=6 March 2009}}</ref> Other, more frequent supply spacecraft do not require this adjustment as they are substantially higher performance vehicles.<ref name="Worldbook at NASA">{{cite web|last=Oberg|first=James|year=2005|title=International Space Station|url=http://www.worldbookonline.com/pl/referencecenter/article?id=ar279523|access-date=3 April 2016|publisher=World Book Online Reference Center}}{{Dead link|date=October 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name="nasa.gov-iss-environment">{{cite web|title=ISS Environment|url=http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archive-url=https://web.archive.org/web/20080213164432/http://pdlprod3.hosc.msfc.nasa.gov/D-aboutiss/D6.html|archive-date=13 February 2008|access-date=15 October 2007|url-status=dead|publisher=[[Johnson Space Center]]}}</ref>

Atmospheric drag reduces the altitude by about 2&nbsp;km a month on average. Orbital boosting can be performed by the station's two main engines on the ''Zvezda'' service module, or Russian or European spacecraft docked to ''Zvezda''{{'s}} aft port. The Automated Transfer Vehicle is constructed with the possibility of adding a [[Automated Transfer Vehicle#ATV evolution proposals|second docking port]] to its aft end, allowing other craft to dock and boost the station. It takes approximately two orbits (three hours) for the boost to a higher altitude to be completed.<ref name="nasa.gov-iss-environment" /> Maintaining ISS altitude uses about 7.5 tonnes of chemical fuel per annum<ref name="newscientist.com">{{Cite magazine|url=https://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine/|title=Rocket company tests world's most powerful ion engine|last=Shiga|first=David|date=5 October 2009|access-date=10 August 2017|url-status=live|archive-url=https://web.archive.org/web/20230810145849/https://www.newscientist.com/article/dn17918-rocket-company-tests-worlds-most-powerful-ion-engine/|archive-date=10 August 2023|magazine=[[New Scientist]]}}</ref> at an annual cost of about $210&nbsp;million.<ref name="aaESummary20100124">{{cite web|date=24 January 2010|title=Executive summary|url=http://www.adastrarocket.com/EXECUTIVE%20SUMMARY240110.pdf|url-status=dead|archive-url=https://web.archive.org/web/20100331171616/http://www.adastrarocket.com/EXECUTIVE%20SUMMARY240110.pdf|archive-date=31 March 2010|access-date=27 February 2010|publisher=Ad Astra Rocket Company}}</ref>

[[File:ISS orbits 04132013.jpg|thumb|upright=1.3|Orbits of the ISS, shown in April 2013]]

The Russian Orbital Segment contains the Data Management System, which handles Guidance, Navigation and Control (ROS GNC) for the entire station.<ref name="Navigation">{{Cite web|url=https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/International_Space_Station/DMS-R_ESA_s_Data_Management_System|title=DMS-R: ESA's Data Management System|publisher=[[European Space Agency]]|url-status=live|archive-url=https://web.archive.org/web/20230811163127/https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/International_Space_Station/DMS-R_ESA_s_Data_Management_System|archive-date=11 August 2023}}</ref> Initially, ''Zarya'', the first module of the station, controlled the station until a short time after the Russian service module ''Zvezda'' docked and was transferred control. ''Zvezda'' contains the ESA built DMS-R Data Management System.<ref name="EsaComputer">{{Cite magazine|url=https://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|title=Exercising Control 49 months of DMS-R Operations|last1=Reimers|first1=Claus|last2=Guyomard|first2=Daniel|date=August 2004|publisher=[[European Space Agency]]|url-status=live|archive-url=https://web.archive.org/web/20230811162355/https://www.esa.int/esapub/onstation/onstation17/os17_chapter6.pdf|archive-date=11 August 2023|magazine=on Station|volume=17}}</ref> Using two fault-tolerant computers (FTC), ''Zvezda'' computes the station's position and orbital trajectory using redundant Earth horizon sensors, Solar horizon sensors as well as Sun and star trackers. The FTCs each contain three identical processing units working in parallel and provide advanced fault-masking by majority voting.